English verbs have five basic forms:
the base, - S, -ing, past,
and past participle
forms.

The
past
participlesfor
regular verbs are the same
as theirpast forms (look-looked-looked
and study-studied-studied), for example. For
irregularverbs, the past and
past participleforms
are different (for
example, be- was/were-beenandgo-went-gone).

The past participle is commonly used
in
several situations:

1.

Past
participles are used as part of
the
present andpastperfect
tenses (both
"regular"
and continuous).

The non-continuous present perfect tense
uses hasor have
+ the past
participle;
the present perfectcontinuous
tense
uses has or have +
been (the
pastparticiple of BE) + the
- ing form of the main verb.

Examples:

He has (He's) taken a vacation. /He has (He's) been taking a vacation.

I have (I've) taken my medicine.I have (I've) been taking that medicine for three
days.

The
non-continuous past perfect tense
uses
had +the past participle;
the past perfect continuoustense uses had
+
been + the - ing form
of themain verb.

Examples:

She had (She'd) lived here for 10 yearswhen I met her.

She had (She'd) been living here for
10 yearswhen I met her.

He had (He'd) waited a long time before
he left.

He
had (He'd) been waiting a long time
before he
left.

2.

Past
participles are also used to make
one of thepast forms for the modal verbs
(modal auxiliaries).These forms use a modal +
have + the past participle.

Examples:

could have gonemay have
beenshould have knownmight have
seenwould have writtenmust have
forgotten

3.

Another use
for past participles is
as participialadjectives (verb forms used as adjectives).

Participial adjectives may be used both
singlyand in phrases.

Examples:

We were bored / excited /
interested.

We
were bored with / excited about /
interested inthe movie.

It's broken / gone / done.

It's broken into two pieces / gone from
whereI usually put it / done by machine, not
by hand.

Abandoned, he didn't know what to do.

Abandoned by everyone he had considered
to behis friends, he didn't know what to do.

4.

One more use
of past participles is
in making thepast form of infinitives (to
+ the base form).

Examples:

to be / to have been;to
live / to have lived;to go / to have gone;to have / to have had.

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Special Notes:

1.

In the "modal perfect" tenses,
the modal auxiliaryand have are usually contracted in spoken English(though this is not as common in written
English):

could have --> could've; may
have --> may've; might have --> might've;must have --> must've; should
have --> should've; would have -->
would've

When
've is spoken quickly in casual conversation,the sound changes to something like "a"
(the secondvowel sound in "sofa").
The common word "of" ispronounced the
same way in quick, casual speech.Because of this,
people sometimes write wrong formssuch as *could
of, *may of, *might of, etc.

2.

Both -
ing forms (present
participles)
and pastparticiples
are used as adjectives
(for example,boring / bored and exciting / excited),
butthemeanings are not the
same:

He's
boring = He bores
someone.

He's
bored = Something
(or someone)
bores him.

They're exciting =
They excite someone.

They're excited = Something
(someone) excites him.

3.

The past infinitive is not very common
except invery formal writing or when it is important
toshow two different times:

Tennyson: "'Tis better to have
loved and lost thannot to have
loved at all." (This is formal language.Also,
the poet makes a contrast between
now--"'Tis
better"
[Itis better]--and
the past--"to haveloved and lost" [loving
and losing were in the past].)